Browsing by Author "Cosanay, H"

Now showing 1 - 13 of 13
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    A computational analysis on convective heat transfer for impinging slot nanojets onto a moving hot body
    Cosanay, H; Oztop, HF; Selimefendigil, F
    Purpose The purpose of this study is to perform computational analysis on the steady flow and heat transfer due to a slot nanojet impingement onto a heated moving body. The object is moving at constant speed and nanoparticle is included in the heat transfer fluid. The unsteady flow effects and interactions of multiple impinging jets are also considered. Design/methodology/approach The finite volume method was used as the solver in the numerical simulation. The movement of the hot body in the channel is also considered. Influence of various pertinent parameters such as Reynolds number, jet to target surface spacing and solid nanoparticle volume fraction on the convective heat transfer characteristics are numerically studied in the transient regime. Findings It is found that the flow field and heat transfer becomes very complicated due to the interaction of multiple impinging jets with the movement of the hot body in the channel. Higher heat transfer rates are achieved with higher values of Reynolds number while the inclusion of nanoparticles resulted in a small impact on flow friction. The middle jet was found to play an important role in the heat transfer behavior while jet and moving body temperatures become equal after t = 80. Originality/value Even though some studies exist for the application of jet impingement heat transfer for a moving plate, the configuration with a solid moving hot body on a moving belt under the impacts of unsteady flow effects and interactions of multiple impinging jets have never been considered. The results of the present study will be helpful in the design and optimization of various systems related to convective drying of products, metal processing industry, thermal management in electronic cooling and many other systems.
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    Analysis of phase change dynamics by using fin in a 3D tall cavity and modeling with artificial neural network
    Örtop, HF; Selimefendigil, F; Cosanay, H
    Computational fluid dynamics studies on phase change process dynamics, heat transfer and fluid flow in a 3D tall cavity are performed by using finite volume method. Both finned and un-finned cases are considered. Thermal transport enhances with higher values of Grashof number while phase change process is further improved by installing a fin within the cavity. The fin and its parameters can be used for thermal management and control of phase change dynamics As compared to no-fin case, 40% and 8% higher melt fraction amounts are obtained by using fin at t = 400 s and t = 1200s. The fin size and its location in the 3D tall cavity is found as an excellent tool for phase transition control. The best phase change process performance is achieved when the fin is used in the middle part of the 3D tall prism as l/W = 0.5, h/W = 0.05 and w/W = 0.4. Dynamics of phase change is estimated by using feed-forward neural networks for finned and un-finned configurations.
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    Thermal energy storage via waste heat from finned heater by using different phase change materials in a closed space
    Öztop, HF; Cosanay, H; Biswas, N; Selimefendigil, F
    In this study, a numerical analysis of the melting of phase change materials (PCMs), is analyzed in a closed space, which is heated from the bottom wall. The heater has a set of fins with constant geometry, placed on the bottom heated wall. The closed space has also two rectangular-shaped containers (placed horizontally), which are attached to the vertical walls at different dimensions and locations. Each of the containers has different types of PCMs, which receive waste heat from the fins. The performance analysis of the combined system is carried out by solving governing equations using the finite volume technique was used to solve the transport equations. The thermal performance of the composite system is assessed for the wide range of geometrical parameters such as length ratios of the fins (Lp), height ratios (c/H), and flow control parameters such as Grashof numbers (Gr). The result showed that the inclusion of PCM containers can effectively utilize the waste heat and can modulate the thermal transport process significantly. The position and size of the fins significantly alter the convective process inside the enclosure. The flow structure shows asymmetric features due to the obstruction by the fins attached to the vertical walls. Too much closure position of the PCM-filled longer fins to the fins assembly leads to the multicellular vortices like 'Be & PRIME;nard cell' due to the strong temperature gradient between the two sets of fins. For the long fins, too much closure position reduces the total melting time. The usage of PCM 2 is always beneficial for faster acclimation energy due to fast melting for any length and position of the fins. Different phase change materials and their melting behaviors are studied first time in this work to get cooling effect of a finned heating system, which is the main originality and the work. Such a concept could be adopted as thermal energy storage (TES) system, which can benefit the reduction in energy losses.
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    Analysis of melting of phase change material block inserted to an open cavity
    Öztop, HF; Cosanay, H; Selimefendigil, F; Abu-Hamdeh, N
    A numerical work has been conducted to explore the effects of opening parameters on melting of phase change material (PCM) during natural convection in a partially open enclosure. A finned heater is located on bottom wall while the remaining parts are insulated. Paraffin wax is used as PCM and two-dimensional time dependent analysis is performed by using the finite volume method for the parameters of location of opening and temperature difference. The governing parameters for the study are chosen for the range of Ra = 1.45 x 10(8) <= Ra <= Ra = 1.97 x 10(8), 0.25 <= w/H <= 0.75 and 0.25 <= c/H <= 0.75. It is found that both opening ratio and opening length are effective parameter on melting time and these can be used as control parameters for improving the energy efficiency. Also, heat transfer can be controlled by using PCM inserted block and opening parameters. Among different cases of opening ratios and locations of opening, the most favorable configuration is obtained at Ra = 1.97 x 10(8), w/H = 0.25, c/H = 0.25 while average heat transfer enhancement by about 60% is achieved. At the lowest and highest value of Rayleigh numbers, the most favorable location of the opening is obtained at c/H = 0.25 in order to have the highest reduction amount of phase completion time.
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    Effects of Inclined Plate in a Channel to Control Melting of PCM in a Body Inserted on the Bottom Wall
    Öztop, HF; Bakir, E; Selimefendigil, F; Gür, M; Cosanay, H
    A two-dimensional time-dependent computational analysis was carried out to examine the effects of inclined plate on melting time of Phase Change Material (PCM) filled square block on the bottom wall of a channel. Solution of the governing equations are performed by using finite volume method. The RT25HC material is chosen as PCM. The study is done for different parameters of inclination angle of the plate and Reynolds number. It is observed that the inclined plate can be used to control of melting time of PCM in a block as well as flow field and temperature distribution in the channel. Using of acceleration angle as theta=110 degrees accelerates the melting time of PCM inside the block. Thus, mass fraction rate increases 4 times with application of inclined thin plate.
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    Experimental Analysis of Melting Behavior of Capric Acid (CA)-Stearic Acid (SA) Eutectic Mixture and its 3D Numerical Solution of Natural Convection in a Cup
    Cosanay, H; Selimefendigil, F; Öztop, HF; Sari, A
    Computational studies were performed to investigate the melting process in a cubical closed space. Capric acid (CA)-stearic acid (SA) eutectic mixture is chosen as a phase change material (PCM). Some thermo-physical properties such as melting temperature, latent heat of fusion, specific heat capacity, thermal conductivity, thermal expansion coefficient, density and viscosity of CA-SA eutectic mixture prepared as PCM were measured. Considering these measured properties, the melting behavior of the prepared eutectic PCM was simulated numerically with finite volume method in a three-dimensional cavity. Non-isothermal heating conditions throughout phase change process of the PCM are considered in the numerical modeling study. It is shown that temperature difference has a significant impact on the melting, while its behavior changes for various cross sections. It is observed that the melting does not change after 80 min for the studied PCM. Significant variations for the melting behavior are observed between 2D and 3D configurations. Melt fraction is only 1.20% higher in 3D case as compared to 2D case at t = 130 min and Gr = 1.8 x 10(5), while this value is 1.08% at Gr = 3.6 x 10(4).
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    Analysis of solidification of phase change material flowing through a channel with backward step: Effects of step curvature
    Öztop, HF; Kiyak, B; Biswas, N; Selimefendigil, F; Cosanay, H
    Thermal energy storage (TES) allows to the conservation of energy, enhancing the overall system efficiency and balancing the supply and demand of energy. This article presents a computational analysis of the solidification process of melted paraffin wax phase change material (PCM) through a partially heated backward-facing step channel partially cooled from the bottom and top. Melted PCM enters through the left opening of the step channel and leaves through the right opening. The study examines two distinct cases: considering sharp stepped or angular corner, and stepped or streamlined corner (of radius r = 20 mm) with the same inlet flow and boundary conditions. A comprehensive numerical model is developed and solved using the finite volume-based computational approach. The overall thermal performance of the model during the solidification process is evaluated for the different Reynolds numbers (Re = 20 and 40) and temperature differences (Delta T = 20 and 25 degrees C) for the different time steps. Furthermore, the effect of backward step curvature on the solidification process is also analyzed. The results revealed that all the parameters (Re, Delta T, and curvature) affect the melted PCM flow structure as well as the solidification process inside the channel. Changing the sharp step corner into a streamlined one at the bottom of the channel led to the lowest lesser flow separation and faster solidification process. Therefore, a well-designed streamlined step corner and its shape could be used to increase the discharging speed of thermal energy storage units meaningfully. Furthermore, such designs, the placement of the heater and cooler location, and step curvature are the guiding factors for controlling the performance of the energy storage. With the change in the curvature, the energy efficiency can be increased and the solidification time is lowered by at least 5 %.
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    Impacts of inclined plate on melting time for phase change material filled blocks: Experimental and numerical analysis
    Öztop, HF; Gür, M; Selimefendigil, F; Cosanay, H
    This study investigates the impact of inclined plates on the melting time of phase change material (PCM)-filled blocks in a channel under turbulent airflow, considering different velocities. The primary objective is to analyse how inclined plates influence the melting process and the time required for complete melting of PCM blocks. Both experimental and numerical approaches are employed using the finite volume method to solve two dimensional time-dependent governing equations. The Reynolds numbers are varied at 40000, 50000, and 60000, while the inclination angle of the plate ranges from alpha = 110 degrees to 130 degrees. RT25HC is selected as the PCM. The findings reveal that inclined plates effectively regulate PCM cube melting times within a block, influencing the flow field and temperature distribution in the channel. Notably, both experimental and numerical results consistently highlight the alpha = 110 degrees inclination angle as the most effective among the considered angles.
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    Effects of fin shapes and orientations with cyclic heating and cooling on melting and solidification of PCM-filled closed space
    Kiyak, B; Öztop, HF; Biswas, N; Cosanay, H; Selimefendigil, F
    Phase-change materials (PCMs) offer an effective way to store and release thermal energy to balance the supply and demand for energy. Both the melting and solidification processes have a major impact on how effectively energy storage works and also it is affected by the thermal conditions of the heating or cooling source. Thermal energy storage systems using (PCMs are often limited by slow melting and solidification rates. The current work explores a novel strategy of cyclic heating and cooling for improving the PCM melting and solidification process combined with variations in fin shapes and orientations, to address these inefficiencies. The fins are heated and cooled following cyclic heating and cooling pattern for three different cycle periods (CP) with same amplitude. As a result, PCM is subjected to cyclic heating and cooling. The finite volume method is employed to analyze the impact of cyclic heating-cooling cycles on PCM performance. An analysis is also conducted on the impact of the relative shape of fins-that is, flat, concave, and convex, positions-vertical and horizontal-on the melting and solidification process under three different cycle periods. By applying a finite volume-based computational approach, the numerical model is solved. It is observed that the overall thermal performance of PCM-based energy storage is modulated by the cyclic heating-cooling arrangements. With this, melting time is reduced by 47.1 % compared to horizontal fin arrangement. When the fin pair is arranged vertically (theta = 0 degrees), with the increase in the cycle period to CP3, the amount of stored energy (during the heating cycle) is about 24.7 %. Similarly, the amount of stored energy recovery (during the cooling cycle) is about 43.6 %. When the fin pair is arranged horizontally (theta = 90 degrees), the amount of energy stored is up to 10 % due to the increase in the cycle periods. Similarly, the amount of stored energy recovery (during the cooling cycle) is about 38.5 %. An improved fin designs, combined with cyclic heating-cooling strategies, present an effective solution to enhance PCM-based thermal energy storage systems.
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    Numerical analysis of conjugate convection heat transfer in an open cavity with different phase change materials surrounded by plexiglass
    Öztop, H; Selimefendigil, F; Cosanay, H; Abu-Hamdeh, N
    Phase change (PC) process and convection inside an open cavity equipped with two different PCMs are analyzed with the finite volume method with ANSYS Fluent. The analysis is conducted for three different Grashof number (Gr) values for fully and partly open configurations. It is observed that the PC becomes fast when the object is closer to the exit for the fully open case. The partly open case results in higher thermal performance improvements while the average Nusselt number (Nu) increment is 94.5% for PCM-18. PC and heat transfer characteristics are influenced by both material and location of the PCM. At Gr = 3.79 x 10(8), the average Nu rises by about 50% when PCM-22 is used instead of PCM-18. Location and type of PCM provide excellent tool for controlling the phase transition and heat transfer dynamics with a fully and or partly open cavity.
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    Analysis of Natural Convection and Melting in a Separated Cavity with Nano-enhanced Phase Change Material filled wall
    Öztop, HF; Cosanay, H; Biswas, N; Selimefendigil, F
    In this study, a new control of the heat transport process utilizing phase-change materials (PCMs), as latent thermal energy storage, and nanofluid flow in a thermal system is explored numerically. The proposed model comprises PCM domain divided square enclosure, filled with two different nanofluids (TiO2 and CuO) heated and cooled, respectively, at the left and right sides of the enclosure. Horizontal walls are adiabatic. The coupled mathematical model comprises phase-change materials, nanofluids, and thermal gradients, which are solved numerically following the finite volume-based approach. The enthalpy-porosity technique is adopted to assess the melting behavior of the PCM domain. The thermo-hydraulic performance of the complex system of nanofluids and the melting process of PCM is assessed for the set of control variables such as Grashof numbers (Gr) and nanoparticle concentration (phi). Analysis revealed that the melting performance of the PCM domain is significantly influenced by the concentration of the nanoparticles on both sides. The results revealed that, for the early stage of the melting process, the thickness of the melted layer strongly depends on the interaction of the thermal gradient inside the cavity. Higher Gr value and phi lead to higher thermal convection in the heated section, which allows the faster melting process of the PCM domain and more amount of thermal energy storage inside the PCM. This transport process further enhances with the increase in the nanoparticles concentrations. A higher Gr value with higher nanoparticle concentrations is always beneficial for the higher amount of thermal energy storage and storage goes up to 35.80%.
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    Effects of cooler shape and position on solidification of phase change material in a cavity
    Öztop, HF; Kiyak, B; Biswas, N; Selimefendigil, F; Cosanay, H
    Background: For balancing the imbalance between the energy supply and demand, phase-change materials (PCMs) provide an efficient means in terms of thermal energy storage and release. The performance of the energy storage is primarily dependent on the melting as well as the solidification process of the storage medium. Faster charging or discharging of the thermal energy is a primary concern for any thermal energy storage unit. On this background, the present study explores the novel approach for enhancing the solidification process of PCM considering the effects of cooler shape (namely semi-circular, triangular, and rectangular) and their position (namely top, side, and bottom) in a molten PCM-filled enclosure. The middle portion of the cooler wall is curved; whereas the remaining cooler wall is straight maintaining the same cooler wall length. Methods: To analyze the solidification process, the involved transport equations are solved numerically following a finite volume-based computational approach using Ansys Fluent solver in conjunction with the appropriate boundary conditions. The computational model is generated for all the geometry comprising different shapes, as well as positions of the cooler wall. The third-order upwind scheme (QUICK) technique is utilized to discretize the momentum and energy equations. This scheme is well capable to accurately capture the gradients in the temperature and flow domains. Furthermore, the semi-implicit pressure-linked equation (SIMPLE) technique is utilised to address the pressure-velocity coupling. The resolved data are then saved as selective variables (U, V, and theta), which undergo post-processing to produce a local thermo-fluid flow field and extract average data. Significant findings: The shape, as well as the position of a cooler, dictates the solidification process in an energy storage system. Thermal energy storage with a triangular-shaped cold wall positioned at the top could be opted as an appropriate design approach of an efficient energy storage system compared to a semi-circular or rectangular-shaped cooler model. The shortest solidification time of PCM occurs when the cooler wall is positioned at the top. The top position of the cooler having a triangular shape with higher Grashof number (Gr) values leads to a faster solidification process. Some ideas for possible future research areas in this field are provided after a comprehensive examination.
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    Analysis of melting of phase change material inserted a block via impinging turbulent slot jet
    Oztop, HF; Gür, M; Selimefendigil, F; Cosanay, H
    PurposeThe purpose of this study is to do a numerical analysis of the jet to a body filled with phase change material (PCM). The melting of the PCM filled body was investigated by the hot jet flow. Four different values of the Reynolds number were taken, ranging from 5 x 103 = Re = 12.5 103. Water, Al2O3 1%, Al2O3 2% and hybrid nanofluid (HNF; Al2O3-Ag mixture) were used as fluid types and the effects of fluid type on melting were investigated. At 60 & DEG;C, the jet stream was impinged on the PCM filled body at different Reynolds numbers. Design/methodology/approachTwo-dimensional analysis of melting of PCM inserted A block via impinging turbulent slot jet is numerically studied. Governing equations for turbulent flow are solved by using the finite element method via analysis and system fluent R2020. FindingsThe obtained results showed that the best melting occurred when the Reynolds number increased and the HNF was used. However, the impacts of using alumina-water nanofluid were slight. At Re = 12,500, phase completion time was reduced by about 13.77% when HNF was used while this was only 3.93% with water + alumina nanofluid as compared to using only water at Re = 5,000. In future studies, HNF concentrations will change the type of nanoenhanced PCMs. In addition, the geometry and jet parameters of the PCM-filled cube can be changed. Originality/valueEffects of impinging jet onto PCM filled block and control of melting via impinging hot jet of PCM. Thus, novelty of the work is to control of melting in a block by impinging hot jet and nanoparticles.